The field of the invention is generally that of microscopes and, more particularly, of portable field inspection microscopes intended primarily for relatively low power inspection of flat butt end surfaces of small cylindrical objects, such as the flat butt end surface of a fiber optics cable, or the like. The need for this type of relatively small, relatively lightweight and, therefore, readily portable field inspection microscope has arisen from the quite recent relatively extensive development of the use of fiber optics cables for communication purposes. This has only recently assumed any substantial measure of significance because until very recently, most long distance intelligence transmission lines, such as used by the telephone company, the government or others active in that field have usually been of the so-called "coaxial cable" type, the wave guide type, or have been of a high frequency broadcast transmission type involving spaced transmitters and receivers and a number of intermittently and interveningly located repeater stations, or the like. The prior art use of such systems has generally involved the providing of a relatively small bandwidth for each transmission channel in the case of a voice transmission and substantially wider bandwidths for each video signal transmission channel, with each transmission channel being appropriately coded at the originating end and being correspondingly decoded and consequently segregated from the signals of all other transmission channels carried by the same transmission line at the destination end. Thus, the number of transmission channels which could be handled by any particular such prior art transmission line was limited by its total frequency transmission bandwidth capability and the bandwidth requirement for each individual signal channel unless multiplexing or time-sharing, or functional equivalent was employed. There was also the problem of the signal of one channel sometimes interferring with the signal of another physically adjacent channel by what is known as "cross talk" or the like. Thus, it can be seen that once all of the available total bandwidth handling capability of a particular transmission line had been used, there was or has been no possibility of adding to its signal channel handling maximum capabilities and the only way to provide for such has been to build additional transmission lines (which, for the purposes of this discussion, are also intended to mean the hereinbefore-mentioned type of system involving prior art ultra high-frequency broadcast transmission of signals on individual effectively adjacent channels.) Such physical expansion of transmission line facilities has been, and is, extremely costly and is further complicated by physical space availability problems in many cases, particularly where they pass through portions of large cities and where they must compete for space with other underground utility and communication installations. In recent years, it has been found that fiber optics cables require a much smaller physical space for the transmission or any total frequency bandwidth than do any of the above-mentioned prior art types of transmission lines and this means that many more channels of audio signals, video signals, computer data signals or any other type (or types) of signals which are desired to be transmitted can be handled in the space formerly occupied by one of the above-mentioned prior art types of transmission lines, thus, not requiring the building of new transmission lines or a greater space availability for multiple such prior art types of transmission lines, but merely requiring replacement of such a prior art transmission line with a new much more effective fiber optics cable.
Such a fiber optics cable can be of a single fiber type or of a multiple fiber type and, in the latter case, the multiple fibers may be encased in a single cladding carrier matrix or, in certain instances, in individual carrier matrices. Also, with respect to each individual light-transmissive fiber, it may be of the monomode (single-mode) or multimode (plural-mode) type.
In a monomode (single-mode) arrangement of a typical representative, but non-specifically limiting form, the light-transmissive fiber (exclusive of cladding) may be extremely narrow or thin in a transverse direction, often being approximately five microns in diameter although this dimension may vary somewhat. The exterior cladding may be of any diameter which is thought to be suitable for cable construction and/or mechanical handling purposes, etc. In this type of monomode fiber, the reason for the extreme narrowness of the light-transmissive central fiber is because the narrowness thereof virtually guarantees that a single ray of light can pass from the beginning of such a narrow fiber to the opposite end thereof substantially without major oblique angular dispersion of multiple light rays and subsequent oblique angular interior reflection along the length of a light -transmissive fiber in the manner of a light-transmissive fiber of greater diameter, such as is the case with what is known as a multimode fiber. Thus, minimal light-losses occur, and no fuzzy or dispersed effect occurs relative to transmitted light pulses traveling from the beginning or input end to the output end of such an extremely narrow monomode light-transmissive fiber. Because of this feature, very high frequencies of light pulses can be transmitted along such a monomode light-transmissive fiber with minimal losses and with the need for any possible optical repeater stations along a very long line being virtually eliminated or greatly reduced.
In the case of multimode light-transmissive fibers, each such fiber is typically of about ten times the diameter of the previously-referred to monomode type of light transmissive fiber--say, approximately of a 50 micron diameter, although not specifically so limited to precisely that diameter, which is to be construed as representative only. Each such multimode light-transmissive fiber transmits multiple rays of light there-along between an input end and an output end thereof in a very efficient manner involving small light losses along the length thereof and some fuzziness or dispersion of light pulses transmitted therealong between an input end and an output end of such a multimode light-transmissive fiber. However, the transmission efficiency of such a multimode light-transmissive fiber is substantially less than that previously mentioned hereinbefore in connection with monomode light-transmissive fibers. Also, limitations with respect to the frequencies of light pulse transmission exist in connection with such multimode light-transmissive fibers to a greater extent than is true of such monomode light-transmissive fibers. This is so because in a multimode fiber, parts of each light pulse are reflected from inside surfaces of the fiber as it travels therealong and thus, such reflected light rays travel a longer distance than other parts of the light pulse moving straight along the light-transmissive fiber. This causes the reflected modes to arrive at the output end of the multimode fiber somewhat later than the unreflected ones, producing in varying degrees a somewhat fuzzy or dispersed pulse at the output end. This may limit the effective distance of multimode fiber pulse transmission, or require effective optical repeater stations dispersed along the length thereof.
In any case, both of the hereinbefore-described types of light-transmissive fibers are much more efficient than other non-optical forms of signal transmission and both types are intended to have splicing operations along the lengths thereof greatly facilitated through the use of the novel inspection microscope of the present invention.
In addition to the hereinbefore-referred to monomode fibers and multimode fibers, the inspection microscope of the present invention can be used for greatly facilitating the splicing of single fiber types of fiber optics cables (whether the single fiber is monomode or multimode) or splicing multiple fiber cables (whether each of the fibers is monomode or multimode, or any combination thereof.)
Incidentally, it should be noted that the light-transmissive fiber may be glass, plastic or any suitable material having a higher index of refraction than the exterior cladding material surrounding same and giving physical "body" to the composite fiber optics cable. This will result in the interior reflection of all interior angularly directed light rays which strike the interface between the fiber and the exterior cladding material at less than an angle which is a function of the difference in the indices of refraction of the fiber and its cladding. This refraction index difference causes the inner light-transmissive to function as a so-called "light pipe", which term will be referred to hereinafter in connection with both the multiple fiber type of fiber optics cable and the single fiber type of fiber optics cable. The multiple fiber type of fiber optics cable will be described first, followed later by the single fiber type of fiber optics cable.
Such a multiple-fiber type of fiber optics cable usually consists of a considerable number of individually separate effectively longitudinally directed and closely laterally adjacent so-called "light pipes" often physically held in position in an appropriate mounting matrix such as a plastic resin for example--often of a transparent or translucent type. Each so-called "light pipe" has an extremely small thickness--much less than any of the signal transmissive portions of a prior art transmission line of any of the types previously mentioned, and each so-called "light pipe" is made of a light-transmissive material, such as glass and/or plastic and usually material, or equivalent, having optical characteristics with respect to refraction and reflection characteristics such that substantially longitudinally directed light rays making up a longitudinal beam of light entering an input end of such a "light pipe" are effectively, largely incapable of passing obliquely through the outer wall of the "light pipe" and thus escaping the "light pipe", but, instead, are substantially reflected back into and/or are effectively retained within the interior of the "light pipe" for transmission forwardly and longitudinally along the length thereof from one end to the other.
The hereinbefore-mentioned interior self-reflection feature of such a "light pipe" prevents loss of interior light so that a modulated light signal can be transmitted over very long distances with minimal losses by such a light pipe which, incidentally, can be of very small cross-sectional area. This is the essential characteristic upon which a fiber optics cable relies because, in the multi-fiber form thereof, many such "light pipes" can be positioned adjacent to one another in a mounting matrix with the entire cable being of much smaller cross-sectional area than has been necessary in the past for any of the hereinbefore-mentioned types of transmission lines which would even being to approach the total message-handling capability (or total frequency bandwidth-handling capability) of such a fiber optics cable, which incidentally, may be of flexible substantially unbreakable construction relatively impervious to corrosion and damage from external weathering, water, chemicals, or the like.
However, in any transmission line, it is necessary to be able to cut into the line at any desired location along its length for adding or removing other lines or various forms of output or input equipment or even for repairing any damaged portion of such a line, and this requires that there be some convenient mode of effectively splicing cut transmission lines to each other in the field and with relatively portable and inexpensive equipment. In the case of a fiber optics cable, this normally requires that a cut end of such a fiber optics cable be perpendicular to the longitudinal direction and have a substantially flat cut butt end so that a similar perpendicular substantially flat butt end of another fiber optics cable portion can be effectively joined or spliced to the first-mentioned fiber optics cable butt end by placing them in virtually complete-area-contact relationship to each other, butt end to butt end. If this is done, there will be no small open spaces between cut ends of individual fiber optics so-called "light pipes" in the two different portions of the fiber optics cable, which would cause severe attenuation or loss of transmitted light and would seriously interfere with the long distance transmission of modulated light carrying signals along such a fiber optics cable.
In such a fiber optics cable, where it is of a type including a number of very closely laterally adjacent longitudinally directed, small cross-sectional area "light pipes", the connection or reconnection of flat butt end surfaces thereof might initially appear to present a small problem with respect to correctly aligning individual light pipes of individual separate channels with each other. This apparent problem can be met and overcome by having the light pipes so closely laterally adjacent that any abutment of the cable ends will align substantially all or most of the "light pipe" ends with other "light pipe" ends and without considering relative rotative positioning of each cable butt end with respect to the other one. Where such a junction is effected and multichannel transmission is accomplished along multiple so-called "light pipes" and the effective separation between different channels is accomplished by time sharing, time division, electronic switching and/or effective commutation arrangements, it will make no difference whether the relative rotative position of one cable butt end is moved relative to another end adjacent cable butt end and all that is necessary is to provide the effective encoding or multiplexing means at the input end and corresponding decoding and demultiplexing means at the output end thereof. Of course, it is also possible to provide fewer or only one effective "light pipe" in a cable with visual inspection means to provide for visual rotative adjustment and alignment of a relatively few such cut "light pipes", or to provide for no such rotative adjustment in the case of a single "light pipe". Any or all of these arrangements or other functional equivalents can be used in such a fiber optics cable where the novel inspection microscope of the present invention is intended for use to inspect for the requisite cable butt end flatness needed for effective splicing or welding of such cable butt ends together.
In the case of a single-fiber type of fiber optics cable, wherein the single fiber is usually centrally-positioned right along the axis of the exterior cladding material, the type of butt end flatness needed for effective splicing of two opposed butt ends, again requires perfect flatness of the two fiber optics cable butt ends to be joined and thus, the novel inspection microscope of the present invention will provide very effective means for checking such cable butt end flatness.
Thus, it is clear that the provision of a small relatively lightweight portable field inspection microscope for inspecting fiber optics cable butt ends for substantially perfect flatness thereof to facilitate the joining of same in the manner mentioned above in a light-loss-minimizing fashion would be extremely desirable, and it is precisely such an easily operated fiber optics cable butt end flatness inspection microscope which is provided by and in the present invention, and which has advantages completely overcoming various prior art disadvantages and limitations and thus making possible the widespread use of fiber optics cables for multiple channel signal transmission having advantages which have been previously referred to and which flow from, and occur by reason of, the specific features of the invention pointed out hereinafter.